Electric switch for magnetic chucks



Dec. 22, 1931. H. E. TRACY ELECTRIC SWITCH FOR MAGNETIC CHUCKS Filed May12 1950 Patented Dec. 22, 1931 UNITED STATES PATENT OFFICE 1 HOWARD E.TRACY, F WORCESTER, MASSACHUSETTS, ASSIGNOR T0 0. S. WALKER COM- PANY,INC., OF WORCESTER, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTSELECTRIC swrrcn FOR MAGNETIC CHUCKS Application filed May 12,

This invention relates to an electric switch particularly designed foruse in connection with magnetic chucks.

It is the object of my invention to provide an improved form of switchby which a chuck may be magnetized and demagnetized, the operation ofwhich is preferably controlled by the movement of some part of themachine to operative or inoperative position.

A further object is to provide a switch for such purposes, so designedthat no flexing of wires or other connections is occasioned by relativemovement of the machine parts during the loading or unloading of thechuck or during the operation of the machine.

My invention further relates to arrangements and combinations of partswhich will be hereinafter described and more particularly pointed out inthe appended claim.

A preferred form of the invention is shown in the drawings, in whichFig. 1 is a side elevation of a portion of a grinding machine having myinvention applied thereto;

Fig. 2 is an enlarged side elevation of my improved switch with thecasing broken away to show the interior construction;

Fig. 3 is a plan view of my improved switch;

Fig. 4 is a detail sectional view, taken along the line 4-4 in Fig. 3;and

Fig. 5 is a diagrammatic view showing the electrical connections.

Referring to the drawings, I have shown my improved switch S mounted onthe frame F of a grinding machine or other similar machine tool. Thecontact device C which cooperates with the switch S is shown as mountedon a vertically adjustable head H adapted to support a grinding wheel orother driven tool.

My improved switch S comprises a casing enclosing a base or block 11preferably formed of wood or other insulating material. A pair ofelongated contact strips 12 and 13 are mounted at the opposite edges ofthe block 11 and are connected at their lower ends to wires 14 and 15.

The wires 14 extend to the magnetic chuck 1930. Serial No. 451,535.

to be controlled and the wires 15 extend to a small electric bulb 16adapted to indicate when the magnetic chuck is energized. The wires 14and 15 are arranged in parallel, so that when the chuck is magnetizedthe bulb 16 will be lighted.

A pair of demagnetizing contact plates 20 and 21 are secured at theupperend of the base 11 and are connected by wires 22 to a pair ofterminals 23 and 24 at the lower end of the base 11. Line wires 25 and26 are connected to the terminals 23 and 24 and extend to a suitablesource of direct current supply, such as a battery, not shown. Theterminal 24 is indicated as a positive terminal and the terminal 23 asthe negative terminal. 1 Consequently the demagnetizing contact plate 21will be positive and the plate 23 will be negative.

An additional pair of magnetizing plates 30 and 31 are connected bycross wires 32 to the terminals 23 and 24, the plate 30 being connectedto the positive terminal 24 and the plate 31 to the negative terminal23.

The contact device C comprises a frame or support firmly secured to theupper portion of the Wheel head or other movable machine member H. Thesupport 40 is provided with a plate 41 of insulating material to which apair of double contact members 44 are secured. Each 'member 44 comprisesa casting having spaced parallel sockets 45 (Fig. 4) to receive ballelements 46 pressed yieldingly outward by coil springs 47. The balls 46are so positioned that one of the balls of each double contact memberengages one of the contact strips 12 or 13 and the other ballsuccessively engages one of the demagnetizing plates 20 or 21 and one ofthe magnetizing plates 30 or 31.

Operation Having described the construction of my improved switch, theoperation and advantages thereof will be easily understood. In theextreme upward or inoperative position of the head H, the contactmembers 44 are beyond the range of the switch S and are thus ininoperative position.

As the head H is moved downward to bring the wheel into contact with thework, one of the balls 46 of each contact member engages one of thestrips 12 or 13 and the other ball of each contact member momentarilyengages one of the demagnetizing plates 20 or 21 and then engages one ofthe magnetizing plates 30 or 31.

The contact strip 12 is made positive by the latter contact and thecontact strip 13 becomes negative. The contact members remain in contactwith the magnetizing plates 30 and 31 so long as the head H is inlowered or operative position.

When the work is completed and the head is raised to permit unloadingand reloading of the chuck, the balls &6 pass from engagement with theplates 30 and 31 to momentary engagement with the demagnetizing plates20 and 21. Such contact causes the strip 12 to become negative and thestrip 13 to become positive, thus reversing the direction of currentthrough the magnetic chuck and demagnetizing the chuck so that the workmay be removed.

Continued upward movement of the heads separates the balls from all ofthe contact strips and plates. The contact with the plates 20 and 21 isthus relatively short, and the demagnetizing current does not flow longenough to remagnetize the chuck by contiln ued reverse flow.

When the head H and contact device C is lowered, the momentaryengagement of the demagnetizing plates 20 and 21 produces noparticiillarly useful eltect, but on the other hand, produces noobjectionable efiect, and such contact is merely negligible.

Having described the operation of my invention, it will be seen that thedesired circuits are made and broken entirely by move ment of the head Hto operative and inoperative position and that the use of separatemanually-operated mechanism is entirely avoided. Furthermore, it will beevident that the switch S and all parts contained therein remains at alltimes in fixed position on the frame F, so that no flexing of connectingwires occurs. This has been found objectionable in certain previoustypes of switches, as repeated flexing of the wires eventually causesbreakage.

Having thus described my invention and the advantages thereof, I do notwish to be limited to the details herein disclosed, otherwise than asset forth in the claim, but what I claim is An electric switch for amagnetic chuck comprising a pair of elongated contact strips connectedto said chuck, a pair of magnetizing contact plates of oppositepolarity, a pair of demagnetizing contact plates of reversed polaritywith respect to said magnetizing plates but aligned therewith, all ofsaid con tact strips and plates being mounted in fixed relation on onepart of a machine tool, and 21 pair of double contact members mounted onanother and relatively movable part of said machine tool, said doublecont-act members each being movable in unison and being operative in oneextreme position to connect one of said contact strips to one of saidmagnetizing plates, whereby the chuck is energized, and said doublecontact members being e:t'- tective by continued movement to furtherpositions to connectsaid contact strips to said demagnetizing plates todemagnetize the chuck and to thereafter break all connections to saidcontact strips and chuck.

In testimony whereof I have hereunto affixed my signature.

HOT WARD E. TRACY.

